Method and Tool for Molding a Composite Pressure Vessel Liner to a Boss

ABSTRACT

A method for molding a composite pressure vessel liner to secure a boss to the liner is described. The method comprises providing a moldable liner having an end section with a neck and a port. A boss is positioned around the neck of the liner and the liner is heated and pressure is applied to mold the liner to form to the shape of the boss. The angle of the molded liner secures the boss in place around the liner and it is able to withstand high pressures. A tool for molding the liner and a method for using the tool is also described. The tool comprises a tool body and a pipe having external threads. The tool body abuts the liner and the boss. Winding the pipe exerts pressure on the liner, which when heated, forces the liner to mold to the shape of the boss.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. Nonprovisional patentapplication Ser. No. 15/617,923, entitled “METHOD AND TOOL FOR MOLDING ACOMPOSITE PRESSURE VESSEL LINER TO A BOSS”, and filed on Jun. 8, 2017.U.S. Nonprovisional patent application Ser. No. 15/617,923 claims thepriority benefit of U.S. Provisional Patent Application Ser. No.62/348,077, filed Jun. 9, 2016. The entire contents of each of theabove-listed applications are hereby incorporated by reference for allpurposes.

TECHNICAL FIELD

The disclosure relates generally to pressure vessels for containingfluids under pressure, and more specifically to molding bosses into theliners of composite pressure vessels.

BACKGROUND

Pressure vessels are commonly used for containing a variety of fluidsunder pressure, such as oxygen, natural gas, nitrogen, propane and otherfuels. Pressure vessels may be made of metal or composite materials.Composite pressure vessels provide several advantages over metallicvessels, including reduced weight and increased resistance to corrosion,fatigue and failure. Typically composite pressure vessels comprise anelastomeric or polymeric liner wrapped with a structural fiber compositeand are designed to withstand high pressures, such as 10,000 psi. Oftenthere is a protective shell around the composite for shielding thecomposite against impact damage. The structural fiber composite isgenerally a fiber reinforced resin matrix material, such as a filamentwound or laminated structure such as fiberglass, carbon fiber or Kevlar™which provides the vessel strength for holding the fluid under pressure.The liner is located on the interior of the composite and provides animpermeable barrier between the interior of the vessel and thecomposite, preventing leakage of the fluid stored inside the vessel andchemical degradation of the composite.

Composite pressure vessels may constructed in a variety of shapes andsizes. Most common, pressure vessels have a cylindrical center sectionwith two domed end sections, however other shapes such as spherical,oblate spheroid (near sphere) and toroidal may also be used. A boss atone or both ends provides a fluid communication port between the outsideand inside of the vessel for loading and unloading fluid from thevessel. The boss also structurally joins the inner liner to the outercomposite shell in a way that prevents fluid from entering the spacebetween the liner and shell. The boss is generally made of metal andcomprises a circular flange or support member at the base of a neck thatprotrudes axially outwardly from the end of the vessel. Theflange/support member is attached to the internal liner. A port isdefined along the central axis of the neck and the flange/support memberfor fluid communication between the interior and exterior of thepressure vessel.

In prior art composite pressure vessels, there are various methods forattaching the boss to the liner. Constructing the liner in multiplepieces, including a cylindrical body piece and two dome-shaped endpieces. A boss may be molded into each liner dome, and then the linerdomes are molded to the cylindrical body piece. In other prior artmethods, the boss may be bonded to the exterior surface of the liner.With another method that is generally only used in low pressureapplications, there may be threads molded to the external surface of theliner at its opening and the boss may be screwed onto the threads.

The interface of the boss, the liner and the composite shell can besubjected to very high pressure from the pressurized fluid within thevessel. This pressure can cause problems at the interface, and may causedetachment of the boss from the liner in one or more areas which reducesthe structural integrity of the vessel. This may also expose thecomposite shell or the surfaces between the inner liner and compositeshell to the fluid contents, may contribute to separation of the shells,and/or may result in leakage from the pressure vessel. It is thereforeimportant the boss be securely fastened to the liner to reduce the riskof such problems.

It is therefore desirable to be able to securely fasten a boss to aliner in a way that prevents separation or leakage even under highpressure, and that is also simple and economical to manufacture.

SUMMARY

In accordance with the disclosure, there is provided a method formolding a boss into the end of a composite pressure vessel liner. Thereis also provided a tool for molding the boss into the end of a compositepressure vessel, and a method for using the tool.

There is provided a method for molding a boss into an end of a liner fora composite pressure vessel comprising the steps of: a) providing amoldable liner having a body and at least one end section, the endsection comprising a neck with a port for allowing fluid communicationbetween an interior and exterior of the liner, and an end wall adjacentthe neck; b) positioning a boss around the neck of the liner, the bosscomprising a flange adjacent the liner end wall, and a neck with aninner surface forming a port having an inner end and an outer end,wherein the neck inner surface forms an outward angle from the inner endto the outer end; and c) applying pressure and heat to the liner endsection to mold the liner neck to abut the boss neck inner surface toform the same outward angle; wherein after the liner has cooled, theoutward angle of the liner neck secures the boss in place around theliner neck.

In some embodiments, the outward angle is 3 to 10 degrees from alongitudinal axis of the liner.

Between steps b) and c), there may be step b.i) which comprisespositioning a moldable disk against an end surface of the boss neck andthe liner neck, and wherein in step c), the moldable disk is molded tothe liner neck to form a continuous piece with the liner neck. In stepb.i), the moldable disk may be secured to the end surface usingfastening members.

Prior to step c), the liner neck may be substantially parallel to alongitudinal axis of the liner. Prior to step c), there may a first gapbetween the liner neck and the boss neck inner surface, and after stepc), there is no first gap. Prior to step c), there may be a second gapbetween the liner end wall and the boss flange inner surface, and afterstep c), there is no second gap. The boss flange inner surface may havean outward angle or an inward angle.

In step c), the liner end wall molds to the geometry of an inner surfaceof the boss flange.

The at least one end section of the liner may be dome-shaped.

The liner may be made of a thermoplastic material, such as high-densitypolyethylene (HPDE). The liner may also be made of nylon, Teflon orpolydicyclopentadiene (PDC-PD).

There is also provided a tool for molding a boss into an end of a linerfor a composite pressure vessel, the liner having a liner neck and theboss having a boss neck, the tool comprising a pipe having externaltapered threads; a tool body surrounding a section of the pipe, the toolbody having a tool body neck in sealing engagement with the section ofthe pipe, the tool body neck having an outer surface for contacting theliner neck, the tool body also having a tool body flange projectingradially from the tool body neck for contacting the boss and/or amoldable disc that is in contact with the boss; and the tool alsocomprising fastening devices for fastening the tool body to the boss;wherein the pipe can be wound with respect to the tool body for applyingpressure to the tool body for molding the liner.

The tool body may further comprise at least one heater for heating theliner.

There is also provided a method for molding a boss into an end of aliner for a composite pressure vessel using the tool described above,comprising the steps: a) inserting the pipe into a port of the linersuch that the tool body neck contacts the liner neck, and the tool bodyflange contacts the boss and/or the moldable disc; b) fastening the to&body to the boss; c) heating the liner end; d) winding the pipe towardsthe liner end to apply pressure to the liner neck to mold the liner neckto the boss to form an outward angle of the liner neck; e) allowing theliner to cool; f) unfastening the tool body from the boss; and g)removing the tool from the liner port; wherein the outward angle of theliner neck holds the boss in place around the liner neck. In step d),the pressure may also mold the liner end wall to form to the geometry ofthe boss. In step c), the moldable disc may also be heated, and in stepd), the pressure molds the disc the liner neck to form a continuouspiece.

BRIEF DESCRIPTION OF THE FIGURES

Various objects and features of the disclosure will be apparent from thefollowing description of certain embodiments of the disclosure, asillustrated in the accompanying drawings. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of various embodiments of the disclosure. Similarreference numerals indicate similar components.

FIG. 1 is a side elevation view of a composite pressure vessel linerhaving a boss molded into each end of the liner.

FIG. 2 is a cross-sectional view of the composite pressure vessel linerof FIG. 1 taken along line A-A.

FIG. 3 is an enlarged view of area B in FIG. 2 illustrating the bossmolded into the composite pressure vessel liner.

FIG. 4 is a front end view of the composite pressure vessel liner andboss of FIG. 1.

FIG. 5 is a side perspective view of a composite pressure vessel linerhaving a boss inserted into each end of the liner but not vet securedwithin the liner.

FIG. 6 is a front end view of the composite pressure vessel liner andboss of FIG. 5.

FIG. 7 is a cross-sectional view of the composite pressure vessel linerand bosses of FIGS. 5 and 6, taken along line C-C of FIG. 6, wherein thebosses are inserted into the ends of the liner but not yet secured inplace.

FIG. 8 is a partial side elevational view of a composite pressure vesselliner and boss being molded into the liner using a molding tool.

FIG. 9 is a cross-sectional view of the composite pressure vessel liner,boss and molding tool of FIG. 8 taken along line D-D.

FIG. 10 is an enlarged view of area E of FIG. 9.

FIG. 11 is a side perspective view of a tool body of a molding tool withheaters.

FIG. 12 is a front elevational view of the tool body of FIG. 11.

FIG. 13 is a cross-sectional view of the tool body of FIGS. 11 and 12taken along line F-F.

DETAILED DESCRIPTION

Various aspects of the disclosure will now be described with referenceto the figures, For the purposes of illustration, components depicted inthe figures are not necessarily drawn to scale. Instead, emphasis isplaced on highlighting the various contributions of the components tothe functionality of various aspects of the disclosure. A number ofpossible alternative features are introduced during the course of thisdescription. It is to be understood that, according to the knowledge andjudgment of persons skilled in the art, such alternative features may besubstituted in various combinations to arrive at different embodimentsof the present disclosure.

With reference to the figures, a composite pressure vessel liner and amethod for incorporating a boss into a composite pressure vessel lineris described.

FIGS. 1-4 illustrate a composite pressure vessel liner 12 having a boss20 incorporated into each end of the liner. The liner has a body 12 cwith end sections 12 d. In the illustrated embodiments, the body iscylindrical shaped and the end sections are dome-shaped, however othersuitable shapes may be used. The end sections 12 d have a neck 12 ethrough which a port 14 is defined that allows fluid communicationbetween the interior and exterior of the liner, and an end wall 12 fadjacent the neck 12 e. The liner can be made of a moldable polymermaterial and may be rotomolded in one piece. The liner may be athermoplastic such as high-density polyethylene (HPDE). Other suitableliner materials include but are not limited to nylon, Teflon, andpolydicyclopentadiene (PDCPD).

As can best be seen in FIG. 3, the boss 20 has a neck 20 a and a flange20 b, the flange extending radially from the neck 20 a. The boss neck 20a has an inner surface 20 h that abuts the liner neck 12 e. The bossflange 20 b has an inner surface 20 c that abuts the liner end wall 12f. The boss neck 20 a and liner neck 12 e angle outwardly from an innerend 14 a to an outer end 14 b of the port 14, shown by angle θ in FIG,3. In some embodiments, the angle is 3 to 10 degrees, however it may beany number greater than zero that allows the boss 20 to be held in placeagainst the liner and still have an opening for the port 14. Thediameter of the boss and the pressure vessel will influence what theoutward angle may be.

Referring to FIG. 3, the liner end wall 12 f abuts against the bossflange inner surface 20 c and has the same geometry as the boss flangeinner surface. This geometry depends on the geometry of the pressurevessel and is calculated based on the optimal geometry for eliminatingany abrupt contour changes in the pressure vessel which would causestress concentrations. The boss flange inner surface 20 c may angleoutwardly, as shown in FIG. 3, or it may include an inward angle, asshown in FIG. 7.

To secure the boss 20 to the liner end section 12 d, the boss ispositioned around the liner neck 12 e and the liner is molded to holdthe boss in place. FIGS. 5 to 7 illustrate the boss 20 placed around theliner neck prior to molding. As can be seen in FIG. 7, prior to molding,the angle of the liner neck 12 a does not match the outward angle θ ofthe boss neck inner surface 20 h. Instead, the liner neck 12 a isgenerally parallel with a longitudinal axis 22 of the liner which allowsthe boss neck to be placed around the liner neck. The difference in theangle of the liner neck and boss neck inner surface creates a first gap24 between the outer end of the boss neck 20 a and liner neck 12 e. Theangle θ of the boss neck inner surface 20 h is the desired angle thatthe liner neck 12 e will form after molding is complete. After molding,there will be no first gap 24 since the liner neck 12 e will form to theangle of the boss neck inner surface 20 h, as shown in FIG. 10.

Prior to molding the liner, the geometry of the liner end wall 12 f maynot match the geometry of the boss flange inner surface 20 c, as shownin FIG. 7. This discrepancy may create a second gap 26 between the bossflange inner surface and the liner end wall. The geometry of the bossflange inner surface 20 c is the desired geometry that the liner endwall 12 f will form after molding is complete. After molding, there willbe no second gap 26 since the liner end wall 12 f will form to thegeometry of the boss flange inner surface 20 c.

As shown in FIGS. 5 to 7, a disc 28 may be placed against an end surface20 e of the boss neck 20 a. The disc 28 includes an inner opening 28 athat aligns with the port 14. In certain embodiments, the disc can bemade of the same material as the liner, i.e. HDPE or another suitablethermoplastic, and can be molded to the liner neck 12 e to prevent theboss from rotating or moving axially with respect to the liner whileapplying the composite material overwrap. Prior to molding, the disc 28may be secured to the outer surface of the boss neck 20 a usingfastening members such as screws or pins that extend through holes 28 bin the disc and holes 20 f in the boss neck, shown in FIGS. 5-7.

During molding, pressure and heat molds the disc 28 to the liner neck 12e, as shown in FIG. 10 where the disc 28 is shown as molded to the linerneck to form one continuous piece with the liner neck. While FIGS. 5 to7 illustrate the disc 28 being fastened to the liner neck using bolts orscrews prior to molding, in FIG. 10 the disc 28 has simply been moldedto the liner neck without requiring bolts or screws. The disc may alsoinclude lips that hook around the outside of the boss neck 20 a (notshown).

Molding Tool

To mold the liner end section 12 d, including the liner neck 12 e andend wall 12 f, to form to the boss 20, a molding toot 30 is used, asillustrated in FIGS. 8-10. In some embodiments, the tool 30 comprises apipe 32 and a tool body 34 surrounding a section of the pipe. Referringto FIGS. 11-13, the tool body 34 comprises a tool body neck 34 a havingan internal surface 34 b that is sealingly engaged with the pipe 32, anda tool body flange 34 c that projects radially from the tool body neck34 a and has an inner surface 34 d. As shown in FIGS. 8-10, an outersurface 34 e of the tool body neck contacts a liner neck internalsurface 12 g. The tool body flange inner surface 34 d contacts the bossneck end surface 20 e and/or the disc 28 if a disc is being used. Theangle of the tool body neck outer surface 34 e may also correspond tothe outward angle θ of the boss neck inner surface 20 h.

To sealingly engage the toot body neck 34 a to the pipe 32, varioussealing mechanisms can be used. The location, type and number of sealsmay vary. In the embodiment shown in FIG. 10, there are two seals 38 and42. The first seal 38 is disposed between the outer surface 32 a of thepipe and the tool body neck internal surface 34 b, The second seal 42 isdisposed between the tool flange inner surface 34 d and the disc 28,when a disc is being used.

The tool body 34 of the molding tool 30 may also include fastener holes46 for receiving fastening devices 36, such as bolts or screws, forfastening the tool body 34 to the boss 20.

The tool 30 may include one or more heaters for heating the liner endsection 12 d and/or disc 28. The heaters may be inserted into the toolbody 34. FIGS. 11 to 13 illustrate an end surface 34 f of the tool bodyflange 34 c having heating fixture holes 44 for receiving heaters. Theheating fixture holes may be positioned in a ring formation as shown inFIG. 12, however other formations may also be used. The tool body flange34 c may also include fastener holes 46 in a ring formation forreceiving the fastening devices 36 for attaching the tool body 34 to theboss 20.

The pipe 32 has an outer surface 32 a with tapered threads 32 b suchthat the pipe can be wound in either direction with respect to the toolbody 34. Winding the pipe towards the tool body exerts pressure on thetool body, which then exerts pressure on the liner 12 and/or disc 28 formolding purposes.

Method for Using the Molding Tool

To use the molding tool to mold the liner 12, the tool pipe 32 isinserted into the port 14 such that the tool body 34 contacts the linerneck 12 e and the boss 20, as shown in FIGS. 8 to 10. The tool body 34is fastened to the boss 20 using the fastening devices 36. The liner endis heated using a heating device, which may be heaters that are locatedwithin the tool body, for example cartridge heaters. The tool pipe 32 iswound towards the liner 12, applying inward pressure to the tool body 34which forces the liner neck 12 e to mold to the shape of the boss neckinner surface. This creates the desired outward angle θ of the linerneck as described above. The pressure also causes the liner end wall 12f to mold to the shape of the boss flange inner surface 20 c. If amoldable disc 38 is present between the disc neck end surface 20 e andthe tool body flange inner surface 34 d, the heat and pressure will moldthe disc to the liner neck 12 e such that the disc forms a continuouspiece with the liner neck.

After the liner is sufficiently molded, the liner is allowed to coolwith the tool in place to set the shape of the liner, After cooling, thetool is removed by unwinding the pipe to release the pressure anddetaching the fastening devices 36. The boss is now secure in placearound the liner neck 12 e and axial movement of the boss with respectto the liner is prevented due to the angle of the liner neck, even whenvery high pressures are applied to the interface from pressurized fluidstored in the vessel. The liner is then wrapped with a compositematerial to finish the vessel, as would be known to a person skilled inthe art.

Alternatively, to mold the liner, pressure can be applied hydraulicallyor pneumatically, and automated equipment may be used.

This method for molding the boss to the liner in a composite pressurevessel can be used on a variety of sizes of vessels that can withstand avariety of operating pressures, including high pressures of 10,000 ormore psi.

The boss may be made of metal or non-metal materials, including but notlimited to alloys of aluminum, steel, nickel or titanium, and compositematerials.

The boss and method for attaching the boss to a composite pressurevessel can be used with various shaped composite pressure vessels,including but not limited to spherical, oblate spheroid and toroidalvessels.

Although the present disclosure has been described and illustrated withrespect to certain embodiments and uses thereof, it is not to be solimited since modifications and changes can be made therein which arewithin the fill, intended scope of the disclosure as understood by thoseskilled in the art.

1-14. (canceled)
 15. A tool for molding and securing a moldable liner toa boss for a composite pressure vessel, the liner having an end sectionwith a liner neck, and the boss having a boss neck, a boss inner surfaceand a boss end surface, the tool comprising: a pipe having externaltapered threads; a tool body surrounding a section of the pipe, the toolbody having: a tool body neck in sealing engagement with the section ofthe pipe, the tool body neck having an outer surface for contacting theliner neck and corresponding to the boss inner surface and the boss endsurface; and a tool body flange projecting radially from the tool bodyneck for contacting the boss and/or a moldable disc that is in contactwith the boss; and fastening devices for fastening the tool body to theboss; wherein the pipe can be wound with respect to the tool body forapplying pressure to the tool body for molding the liner.
 16. The toolof claim 15 wherein the tool body further comprises at least one heaterfor heating the liner.
 17. A method for molding a boss into an end of amoldable liner for a composite pressure vessel using the tool of claim15 comprising the steps: a) inserting the pipe into a port of the linersuch that the tool body neck contacts the liner neck, and the tool bodyflange contacts the boss and/or the moldable disc; b) fastening the toolbody to the boss; c) heating the liner end section; d) winding the pipetowards the liner end section to apply pressure to the liner neck tomold the liner neck to the boss to form an outward angle of the linerneck; e) allowing the liner to cool; f) unfastening the tool body fromthe boss; and g) removing the tool from the liner port; wherein theoutward angle of the liner neck holds the boss in place around the linerneck.
 18. The method of claim 17, wherein in step d), the pressure moldsthe liner end section to form to the geometry of the boss.
 19. Themethod of claim 17 wherein in step c) the moldable disc is also heated,and in step d), the pressure molds the disc to the liner neck to form acontinuous piece.